Water solvent method for esterification and amide formation between acid chlorides and alcohols promoted by combined catalytic amines: Synergy between N-methylimidazole and N,N,N′,N′-tetramethylethylenediamine (TMEDA)

Article abstract of DOI:10.1002/adsc.200600256

An efficient method for esterification between acid chlorides and alcohols in water as solvent has been developed by combining the catalytic amines, N-methylimidazole and N,N,N′,N′-tetramethylethylenediamine (TMEDA). The present Schotten-Baumann-type reaction was performed by maintaining the pH at around 11.5 using a pH controller to prevent the decomposition of acid chlorides and/or esters and to facilitate the condensation. The choice of catalysts (0.1 equiv.) was crucial: the combined use of N-methylimidazole and TMEDA exhibited a dramatic synergistic effect. The catalytic amines have two different roles: (i) N-methylimidazole forms highly reactive ammonium intermediates with acid chlorides and (ii) TMEDA acts as an effective HCl binder. The production of these intermediates was rationally supported by a careful ¹H NMR monitoring study. Related amide formation was also achieved between acid chlorides and primary or secondary amines, including less nucleophilic or water-soluble amines such as 2-(or 4-)chloroaniline, the Weinreb N-methoxyamine, and 2,2-dimethoxyethanamine.

Full text of DOI:10.1002/adsc.200600256

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DOI: 10.1002/adsc.200600256
Water Solvent Method for Esterification and Amide Formation
between Acid Chlorides and Alcohols Promoted by Combined
Catalytic Amines: Synergy between N-Methylimidazole and
N,N,N’,N’-Tetramethylethylenediamine (TMEDA)
Hidefumi Nakatsuji,a Jun-ichi Morita,a Tomonori Misaki,a and Yoo Tanabea,*
a
Department of Chemistry, Schoolof Science and Technool gy, Kwansei Gakuin University, 2–1 Gakuen, Sanda, Hyogo
669-1337, Japan
Fax : (+81)-795-65-9077; e-mail: tanabe@kwansei.ac.jp
Received: May 31, 2006; Accepted: August 8, 2006
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: An efficient method for esterification be-
tween acid chlorides and alcohols in water as sol-
vent has been developed by combining the catalytic
amines, N-methylimidazole and N,N,N’,N’-tetrame-
thylethylenediamine (TMEDA). The present Schot-
ten–Baumann-type reaction was performed by
maintaining the pH at around 11.5 using a pH con-
troller to prevent the decomposition of acid chlor-
ides and/or esters and to facilitate the condensation.
The choice of catalysts (0.1 equiv.) was crucial: the
combined use of N-methylimidazole and TMEDA
exhibited a dramatic synergistic effect. The catalytic
amines have two different roles: (i) N-methylimida-
zole forms highly reactive ammonium intermediates
with acid chlorides and (ii) TMEDA acts as an ef-
fective HClbinder. The production of these inter-
mediates was rationally supported by a careful
1H NMR monitoring study. Related amide forma-
tion was also achieved between acid chlorides and
primary or secondary amines, including less nucleo-
philic or water-soluble amines such as 2-(or
4-)chloroaniline, the Weinreb N-methoxyamine, and
2,2-dimethoxyethanamine.
synthetic methods available. The numerous reported
methods, however, generally require stoichiometric
amounts of tertiary amines such as pyridine and Et3N
as HClscavengers. The use of an equimoalr amount
of wasted organic amine reagent necessitates a large
amount of BOD and COD (biological and chemical
oxygen demands).
Organic reactions in water as solvent have recently
attracted considerable attention from the standpoint
of green and process chemistry.[2] The Schotten–Bau-
mann-type condensation in water as solvent is consid-
ered to be a rational and environmentally benign pro-
cess but, to the best of our knowledge, these methods
are limited to the formation of only a few amides
using reactive amines and/or acid chlorides and there
[3]
are no generalmethods avaial bel for esterification.
We have a long-standing interest in the develop-
ment of mild, practical, and cost-effective esterifica-
tions, amide formations, and thioesterifications be-
tween 1:1 mixtures of carboxylic acids and alcohols,
amines, and thiols, respectively. Recently, as an exten-
sion of pyridine-free sulfonylations (tosylation and
mesylation),[4] the Schotten–Baumann-type method
for these condensations was exploited, wherein specif-
ic amine catalysts such as PhCH2NMe2, BuNMe2, and
Et3N, functioned as efficient promoters.[5] Here, we
present a water-solvent method for esterification be-
tween acid chlorides and alcohols using the combined
catalytic amines, that is, N-methylimidazole and
Keywords: amide formation; esterification; N-meth-
ylimidazole; synergy effect; N,N,N’,N’-tetramethyl-
ethylenediamine; water-solvent method
N,N,N’,N’-tetramethylethylenediamine
(TMEDA)
(Scheme 1). A related amide formation between acid
Esterification and amide formation are well recog- chlorides and primary or secondary amines was also
nized as two important unit processes frequently used performed successfully.
for a wide range of organic syntheses.[1] These reac-
The major problem of Schotten–Baumann-type
tions between carboxylic acid chlorides (the most condensations in water as solvent is the hydrolysis of
popular activated derivative of acids) and alcohols or not only the highly reactive acid chloride substrates
amines are among the most generaland conventional
but also the less reactive ester products. To overcome
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Hidefumi Nakatsuji et al.
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Table 1. Screening of amine catalysts during the esterifica-
tion between PhCOClor PhCH CH2COCland 3-octano.l
2
Scheme 1. Esterification and amide formation between acid
chlorides and alcohols in water solvent promoted by the
combined catalytic amines, TMEDA and N-methylimida-
zole.
Entry
Catalyst
Yield [%]
A
B
1
2
3
4
5
6
7
8
none
Et3N
BnNMe2
BuNMe2
DMAP
TMEDA
N-methylimidazole
Et3N, DMAP
Et3N, TMEDA
Et3N, N-methylimidazole
DMAP, TMEDA
DMAP, N-methylimidazole
TMEDA, N-methylimidazole
trace
trace
trace
trace
41
10
trace
15
9
26
47
38
32
39
38
32
38
33
48
39
56
68
55
43
85
9
10
11
12
13
72
hydrolysis of both these acid chlorides was sufficiently
circumvented when the pH of the water was main-
tained between 11.0 and 12.0. As expected, both
PhCO
A
G
Figure 1. Esterification system in water solvent using dual
microfeeders equipped with a pH controller.
(no reaction) under identicalconditions.
The present reaction system is illustrated in
Figure 1. R1COClwas added to the mixture of R OH
2
this critical issue, we applied a pH controlled protocol and a catalytic amine (0.1 equiv.) in water at 20–258C
for the reaction system. First, we checked the stability for 1 h, using one microfeeder apparatus equipped
of PhCOCland PhCH CH2COClin water at 20–25 8C with a syringe. Aqueous KOH solution was simultane-
2
in the absence of amine catalysts and/or 1-octanol; ously added to the mixture using another microfeeder
Scheme 2. Plausible mechanism for the synergy effect of TMEDA and N-methylimidazole.
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Esterification and Amide Formation between Acid Chlorides and Alcohols
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apparatus equipped with a syringe to maintain the pH
at 11.5 accurately; a pH controller was used to adjust
the timing of the addition of aqueous KOH solution.
The initialscreening of amine cataylsts was guided
by the benzoylation of 3-octanol using PhCOCl (A)
(Table 1). The use of simple monoamines such as
Et3N (the most common tertiary amine) as well as the
absence of the catalyst, failed to promote the reaction
(entries 1–4). Specific amines, DMAP (a super acyla-
tion catalyst),[1] TMEDA (an effective diamine for
benzoylation),[6] and N-methylimidazole (a new acyla-
tion agent),[7] also produced disappointing results (en-
tries 5–7). Surprisingly, the combined use of different
amines exhibited a dramatic synergistic activity (joint
action of amines). The increasing order of yield for all
six possible combinations is as follows (entries 8–13);
(i) Et3N and TMEDA, (ii) Et3N and DMAP, (iii) Et3N
and N-methylimidazole, (iv) DMAP and N-methyl-
imidazole, (v) DMAP and TMEDA, and (vi)
TMEDA and N-methylimidazole. Thus, the best yield
was obtained with TMEDA and N-methylimidazole
[case (vi)]. With regard to the pH value, 11.5 (85%)
produced much better results than 11.0 (33%) and
12.0 (39%) under the same conditions as entry 13.
The present synergy was also observed in the case of
PhCH2CH2COCl(B), tahlough not to the same
extent. Eventually, we chose the combined base cata-
lysts, TMEDA and N-methylimidazole.
A plausible mechanism for the present observation
is as follows (Scheme 2). In the organic phase, the N-
methylimidazole catalyst captures an acid chloride
(R1COCl) to form a highly reactive acyl imidazolium
intermediate A, which in turn condenses with an alco-
2
hol(R OH) to produce the desired ester, while re-
leasing TMEDA·HCl
B into the water phase.
TMEDA might chelate with the alcohol through tight
bidentate hydrogen bonds. In the water phase, B is
neutralized by KOH with regeneration of the
TMEDA in the organic phase. Note that the two
amines have different roles: N-methylimidazole acti-
vates the acylcholride, whereas TMEDA acts as an
HClscavenger.
Scheme 3. 1H NMR monitoring study using a 1:1 mixture of
PhCH2CH2COCland N-methylimidazole in CD3CN.
As depicted in Scheme 3, a careful 1H NMR
(300 MHz) monitoring study exemplified by a 1:1
mixture of PhCH2CH2COCland N-methylimidazole
in CD3CN at À508C rationally supported the present
hypothesis; the generation of acylimidazolium inter- using the present method (Table 2). The salient fea-
mediates A with N-methylimidazole was unambigu- tures are as follows. (i) Several primary and secondary
ously detected (Figure 2); N-methylimidazole [d= alcohols underwent smooth esterification with
3.64 (s, 3H), 6.92 (d, 2H, J=18.9 Hz), 7.38 (s, 1H)] PhCH2CH2COCl in excellent yield (entries 1–8). (ii)
and A [d=3.02 (t, 3H, J=7.57 Hz), 3.44 (t, 3H, J= Water-soluble methallyl and furfuryl alcohol required
7.57 Hz), 3.96 (s, 3H), 7.53 (s, 1H), 7.86 (s, 1H), 10.94 a small amount of EtOAc as co-solvent in order to
(s, 1H)]. The apparent downfield chemical shift of N- sufficiently extract the alcohol into an organic phase
methylimidazole moieties in A is related to the higher (entries 9 and 10). (iii) The reaction of severaltypes
acylation reactivity of the present system.
of acid chlorides and alcohols proceeded in good to
These results indicate that esterifications between excellent yield, without loss of their functionalities
various acid chlorides and alcohols were successful (entries 11–20). (iv) Two usefulsynthetic pyrethroids,
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Hidefumi Nakatsuji et al.
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Table 2. . Esterification of various substrates in water as sol-
vent using the combined amine catalyst, N-methylimidazole
and TMEDA.
Table 3. Amide formation from various substrates in water
as solvent using the combined amine catalyst, N-methylimi-
dazole and TMEDA.
Entry R1COClR
2OH
Yield [%]
Entry
1
R1COClNHR
2R3
Yield [%]
92
1
2
98
98
3
90
2
3
84
81
4
95
5
6
82
99
4
72
7
85
5
6
7
8
75
8
92
83[a]
91[a]
99[a]
9
53 (90[a])
97[a]
10
11
98
9
99
12
13
94[b]
96
10
11
80
98[a]
14
15
16
89[b]
95
12
99
68 (42[b])
81[a]
72
13
14
17
18
81
93
15
96
98
16
19
93
[a]
Solvent: H2O (10 mL)/EtOAc (1 mL).
Without TMEDA and N-methylimidazole.
20
75[a,c]
[b]
[a]
Solvent: H2O (10 mL)/EtOAc (1 mL).
Reaction time: 2 h.
Without loss of optical purity.
yield. (ii) Note that weakly nucleophilic anilines such
as 4- and 2-chloroanilines also produced satisfactory
results (entries 3 and 4), because conventional reac-
tions often were unsuccessful.[8] (iii) Water-soluble
[b]
[c]
chlovaporthrin and permethrin, were successfully pre- amines including the important Weinreb amine under-
pared (entries 18 and 19). went smooth amide formation under identicalcondi-
Finally, we applied the present protocol to amide tions using EtOAc as co-solvent, along with the pres-
formation (Table 3). The salient features are as fol- ent esterification (entries 7 and 8). (iv) When using
lows. (i) In every case examined, the desired reaction BnNMe2 or BuNMe2 catalyst, which is effective for
proceeded successfully using several aromatic and ali- sulfonylation in water as solvent,[4] the reaction failed
phatic amines and acid chlorides in good to excellent to proceed.
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Esterification and Amide Formation between Acid Chlorides and Alcohols
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tanol(651 mg, 5 mm),ol
N-methylimidazole (41 mg,
0.5 mmol), TMEDA (58 mg, 0.5 mmol), and K2CO3 (1.04 g,
7.5 mmol) in water (10 mL) at 20–258C during 1 h. Aqueous
5M KOH solution (ca. 2.0–3.5 mL) was simultaneously
added to the mixture using another microfeeder apparatus
to strictly maintain the pH at 11.5; the pH controller was
used to adjust the timing of the addition of
PhCH2CH2COCl. The mixture was stirred at the same tem-
perature for an additional30 min. Water was added to the
mixture, which was extracted with EtOAc. The organic
phase was washed with 1 N HCl, brine, dried (Na2SO4), and
concentrated to give the desired ester, 1-octyl3-phenyplro-
panoate[9]; yield: 1.28 g (98%). The obtained crude ester
was sufficiently pure. The other esters, if necessary, were pu-
rified by distillation or silica-gel column chromatographic
purification.
In conclusion, we have developed a water-solvent
Schotten–Baumann-type method for esterification
and amide formation, between acid chlorides and al-
cohols, and amines, respectively. In clear contrast to
the related sulfonylations, an apparent synergy effect
of the calalytic amines, N-methylimidazole and
TMEDA was observed. Since hazardous amines can
be reduced to catalytic amounts, the present protocol
will provide a new approach to a cost-effective, and
environmentally benign process for esterification and
amide formation.
Experimental Section
Additions of acid chlorides and KOH aqueous solution were
performed using a microfeeder apparatus (Furue Science
JP-S-W2 and JP-S5, respectively) (see Figure 1). The control
of pH was performed using a pH controller apparatus (Toko
ChemicalLaboratoried Co., Ltd. TDP-200 L). Mteilng
points were determined on a hot-stage microscope appara-
tus (Yanagimoto) and were uncorrected. NMR specta were
recorded on a JEOL ALPHA400 spectrometer, operating at
Typical Procedure for Esterification using a Water-
Soluble Alcohol (Table 2, entry 9).
Using
a microfeeder (see Figure 1), PhCH2CH2COCl
(1.26 g, 7.5 mmol) was added to a stirred suspension of 2-
methylpro-2-en-1-ol (360 mg, 5 mmol), N-methylimidazole
(41 mg, 0.5 mmol), TMEDA (58 mg, 0.5 mmol), and K2CO3
(1.04 g, 7.5 mmol) in water (10 mL) and EtOAc (1 mL) at
20–258C during 1 h. Aqueous 5M KOH aqueous solution
(ca. 2.0–3.5 mL) was simultaneously added to the mixture
using another microfeeder apparatus to strictly maintain the
pH at 11.5; the pH controller was used to adjust the timing
of the addition of PhCH2CH2COCl. The mixture was stirred
at the same temperature for 30 min. Water was added to the
mixture, which was extracted with EtOAc. The organic
phase was washed with 1 N HCl, brine, dried (Na2SO4), and
concentrated to give the desired ester; yield: 915 mg (90%).
The obtained crude ester was sufficiently pure.
1
400 MHz for H NMR and 100 MHz for 13C NMR. Chemical
shifts (d ppm) were reported downfield from tetramethylsi-
lane (0 ppm) for 1H NMR and relative to CDCl3
(77.00 ppm) for 13C NMR. IR spectra were recorded on
JASCO FT/IR-8000 and/or FT/IR-5300 spectrophotometer.
Mass spectra were measured on a JEOL JMS-T100 LC spec-
trometer.
The following esters and amides obtained in this paper
[9]
are known compounds: 1-octyl3-phenyplropanoate,
9-
[10]
decen-1-yl3-phenyplropanoate,
6-chlorohexyl 3-phenyl-
[10]
propanoate,[10] 2-hexyn-1-yl3-phenyplropanoate,
ethyl6-
(3-phenylpropanoyloxy)hexanoate,[10] phenyl3-phenypl ropa-
noate,[11] 1-phenylethyl 3-phenylpropanoate,[12] methallyl 3-
phenylpropanoate,[13] 1-octyl cyclohexanecarboxylate,[14] 1-
Typical Procedure for Amide Formation (Table 3,
entry 1).
[15]
[10]
octyl3,3-dimethyblutanoate,
1-octylbenzoate,
3-octyl
1-ethynyl-2-methyl-2-
benzoate,[16] 1-octylmethacryalte,
[17]
Using
a microfeeder (see Figure 1), PhCH2CH2COCl
(1.26 g, 7.5 mmol) was added to a stirred suspension of N-
methylaniline (535 mg, 5 mmol), N-methylimidazole (41 mg,
0.5 mmol), TMEDA (58 mg, 0.5 mmol), and K2CO3 (1.04 g,
7.5 mmol) in water (10 mL) at 20–258C during 1 h. Aqueous
5M KOH solution (ca. 2.0–3.5 mL) was simultaneously
added to the mixture using another microfeeder apparatus
to strictly maintain the pH at 11.5; the pH controller was
used to adjust the timing of the addition of
PhCH2CH2COCl. The mixture was stirred at the same tem-
perature for 30 min. Water was added to the mixture, which
was extracted with EtOAc. The organic phase was washed
with 1 N HCl, brine, dried (Na2SO4), and concentrated to
give the desired amide; yield: 1.10 g (92%). The obtained
crude ester was sufficiently pure.
pentenyl 3-(2,2-dichloroethenyl)-2,2-dimethylcyclopropane-
carboxylate (chlovaporthrin: a vaporthrin analogue),[18] 3-
phenoxybenyl 3-(2,2-dichlorovinyl)-2,2-dimethylcycloprop-
anecarboxylate (permethrin),[19] N-carbobenzoxy-l-proline
phenylmethyl ester,[20] N-methyl-N-phenyl-3-phenylpropan-
amide,[21] N-phenyl-3-phenylpropanamide,[22] N-(4-chloro-
phenyl)-3-phenylpropanamide,[23] N-(2-chlorophenyl)-3-phe-
nylpropanamide,[23] N-[(S)-1-phenylethyl]-3-phenylpropan-
amide,[10] N-(3-phenylpropionoyl)piperidine,[10] N-methoxy-
[24]
N-methyl3-phenyplropanamide,
N-(2,2-dimethoxyethyl)-
3-phenylpropanamide,[25] N-methyl-N-phenylbenzamide,[26]
N-phenylbenzamide,[27] N-benzoylpiperidine,[10] N-methyl-N-
phenylcyclohexanamide,[28] N-phenylcyclohexanamide,[29] N-
cyclohexanecarbonylpiperidine,[10] N-methyl-N-phenyl-3,3-
dimethylbutanamide,[30] N-phenyl-3-(2,2-dichlorovinyl)-2,2-
dimethylcyclopropanamide.[31]
Supporting Information
Characterization data for 3-octyl3-phenyplropanoate, fur-
furyl 3-phenylpropanoate, 3-octyl cyclohexanecarboxylate,
3-octyl 3,3-dimethylbutanoate, 3-(2,2-dichloroethenyl)-2,2-
Typical Procedure for Esterification (Table 2,
entry 1).
Using
a
microfeeder (see Figure 1), PhCH2CH2COCl
dimethyl-1-ethynyl-2-methyl-2-pentenyl
cyclopropanecar-
(1.26 g, 7.5 mmol) was added to a stirred suspension of 1-oc-
boxylate and 3-phenoxybenyl 3-(2,2-dichlorovinyl)-2,2-dime-
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Hidefumi Nakatsuji et al.
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thylcyclopropanecarboxylate are available in the Supporting
Information.
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Acknowledgements
This research was partially supported by Grant-in-Aids for
Scientific Research on Basic Areas (B) “18350056”, Priority
Areas (A) “17035087” and “18037068”, and Exploratory Re-
search “17655045” from the Ministry of Education, Culture,
Sports, Science and Technology (MEXT). We thank Kuraray
Co. Limited., for generous gift of methyl dichlorovinylcrysan-
themate.
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